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Motor neuron diseases are neurological disorders that affect the nerves in the brain and spinal cord. Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disease, affecting both upper and lower motor neurons, resulting in profound muscle weakness and debility. This activity describes the findings of nerve conduction tests and needle electromyography, the indispensable role these findings serve in confirming a diagnosis of ALS, and the importance of an interdisciplinary team approach in treating this condition. Objectives: Determine the classification of motor neuron diseases, focusing on the most common motor neuron disease, amyotrophic lateral sclerosis. Assess the clinical presentation of amyotrophic lateral sclerosis. Determine the indications for EMG for amyotrophic lateral sclerosis. Communicate the electrodiagnostic findings of amyotrophic lateral sclerosis and its importance in diagnosis and management of the disease. Access free multiple choice questions on this topic.

Motor neuron disorders can be thought of as residing on a spectrum, whether upper motor neurons, lower motor neurons, or both are affected. Motor neuron diseases include amyotrophic lateral sclerosis (affects both upper and lower motor neurons), primary lateral sclerosis (affects upper motor neurons), progressive muscular atrophy (affects lower motor neurons ), progressive bulbar palsy (affects lower motor neurons), spinal muscular atrophy (affects lower motor neurons), and post-polio syndrome (affects lower motor neurons). Motor neuron disease is used interchangeably with amyotrophic lateral sclerosis (ALS), as ALS is the most common adult-onset presentation of this disease.[1][2][3] ALS is a neurodegenerative disorder leading to weakness of the bulbar, thoracic, limb, and abdominal muscles with sparing of sensory function. Death usually occurs within 2 to 5 years from respiratory failure. Roughly 85 to 90% of ALS cases are sporadic, with about 10% being of familial origin. According to the 2014 US Census data, the prevalence of ALS was 5 per 100,000 people.[4][5][6] Though there is variation in clinical presentation, the majority of the patients present with asymmetric limb weakness (80%) or bulbar dysfunction (20%). Bulbar dysfunction can manifest as dysphagia (trouble swallowing) and dysarthria (trouble speaking). There is progressive spread to other body areas with accompanying upper and lower motor neuron findings. Upper motor findings include spasticity, hyperactive reflexes, and a positive Babinski sign. Lower motor neuron signs include muscle atrophy, weakness, flaccid paralysis, absent reflexes, fasciculations, and fibrillations.[7][8] Patients can also display changes in behavior due to frontotemporal dysfunction, and about 15% of patients develop frontotemporal dementia. Some patients may also present with Pseudobulbar affect, which is dysregulation of emotional responses exhibited by excessive laughter or crying. Many other neurological disorders, such as strokes, Alzheimer’s disease, and multiple sclerosis, also present with pseudobulbar affect.[7][9]

Patients can also display changes in behavior due to frontotemporal dysfunction, and about 15% of patients develop frontotemporal dementia. Some patients may also present with Pseudobulbar affect, which is dysregulation of emotional responses exhibited by excessive laughter or crying. Many other neurological disorders, such as strokes, Alzheimer’s disease, and multiple sclerosis, also present with pseudobulbar affect.[7][9] Once the diagnosis of ALS is suspected, electrodiagnostic testing is needed. Electrodiagnostic testing assesses the integrity of lower motor neurons and is crucial to diagnosing motor neuron disease, as neuroimaging and laboratory studies are normal oftentimes. Nerve conduction studies (NCS) and needle electromyography (EMG)  are important for supporting the diagnosis of ALS and ruling out other potential mimics of the disease. Some disorders that can mimic motor neuron disease are multifocal motor neuropathy with conduction block, chronic inflammatory demyelinating polyradiculoneuropathy, central nervous system tumors, multiple sclerosis, and polyradiculopathy, among others.[10] It is important to rule out such mimics with NCS and needle EMG as the treatment regimens and prognosis differ among the varying disorders. Since the prognosis of ALS is poor, it is imperative to accurately diagnose the disorder to appropriately manage the associated symptoms involved and develop a treatment plan.

As with any procedure that involves introducing a foreign substance into the body, there is a risk of infection. The risk of infection with needle EMG is very low, less than 1 in 10,000.[12] There is also a risk of bleeding, which is why EMG should be avoided in patients with severe bleeding disorders.

Because there is no cure for ALS and the prognosis is grave, clinicians must diagnose the disease with confirmation by NCS and needle EMG as soon as possible so that the appropriate interventions can be taken. There are only a few approved FDA treatments for ALS. Riluzole blocks glutamate release from neurons and has been shown to prolong survival by a few months. Riluzole can cause an elevation in liver enzymes; therefore, liver function testing should be ordered before administering this medication, as well as periodically.[1] A combination of dextromethorphan and quinidine sulfate has been approved for pseudobulbar effect. It is contraindicated in patients using monoamine oxidase inhibitors, and caution should be taken with patients on selective serotonin reuptake inhibitors due to the risk of serotonin syndrome.[3] Edaravone, a free radical scavenger, is a recently approved drug that decreases oxidative stress, contributing to neuron cell death. It has been shown in some clinical trials to slow the functional decline in ALS patients.[16] The treatment plan should include a multidisciplinary approach to managing a patient’s symptoms and improving overall function and quality of life. Physical and occupational therapists can assist with maintaining mobility and improving functional ability, allowing patients to remain as independent as possible with their activities of daily living. Patients can benefit from exercise regimens that prevent joint contractures, manage spasticity, and increase mobilization. Therapists can also provide recommendations for bracing, wheelchairs, and home equipment. Speech therapists are important for monitoring a patient’s swallowing and assisting those with difficulty speaking. Speech therapists can recommend assistive devices to help patients communicate more efficiently. Respiratory therapists are needed to monitor respiratory function and the need for non-invasive ventilation. Patients who exhibit excess salivation may require anticholinergic medications. Patients and their families should undergo psychosocial counseling to help with the emotional toll of the disease.[3]  For patients to be treated in an appropriate and timely manner, clinicians need to confirm the diagnosis of ALS with NCS and needle EMG studies, as well as rule out other possible etiologies.